In many fields of endeavor, there is a need to quickly and objectively measure the color of a material or an object, or to compare the colors of different materials or objects with each other or with a reference standard. For example, in matching paint colors in automobile repair shops or in quality control of manufacturing operations.
Although there have been many devices, methods and techniques developed for this purpose, generally they have fallen into two categories: first are those which are simple and subjective and second are those which are objective but are also complex and expensive.
In the first category are the familiar color chips and charts such as found in paint stores and the like. Although simple and inexpensive, these methods are subjective in that they depend on the visual acuity and judgement of the user as well as the lighting of the environment where the color evaluation is made. Also, as a practical matter, the number of colors from which to choose is usually limited.
In the second category, there have many devices designed to objectively measure or compare colors. Those which effectively performed their functions have been complex and very expensive. Many are large laboratory instruments having separate bulky or bench-mounted components. Others are smaller self-contained units but which contain high-precision optical components and complex electronic circuitry for performing sophisticated color spectrum analysis. The following inventions are briefly described as examples of the second category,
U.S. Pat. No. 5,838,451 discloses an apparatus for the measurement of spectral reflectance or spectral absorbance of an object or a material. The reflectance apparatus comprises multiple LEDs surrounding a photosensor, all mounted on a common substrate, and a lens for coupling light to and from the object.
U.S. Pat. No. 5,844,680 also discloses apparatus for measuring and analyzing spectral radiation. It discloses three embodiments comprising: (1) multiple LED light sources with a single sensor, (2) a single light source with multiple sensors, and (3) multiple sources and sensors. In each case the wavelength spectra of the multiple sources or sensors overlap to provide full spectrum color measurement within the range of interest.
U.S. Pat. No. 5,851,113 discloses a system comprising a probe containing a plurality of optical fibers connected to a color measurement system. The patent describes various means of color measurement, including multicolored light sources (RGB), and various analysis techniques.
U.S. Pat. No. 5,690,486 discloses a lightweight, handheld, battery powered device for detecting tooth colors. The device comprises a main body, which includes device electronics, and a wand comprising a fiberoptic bundle for placing against the tooth. The main body contains three LED's providing three primary colors (RGB) and a photo detector all optically coupled through the fiber optics wand to its tip.
U.S. Pat. No. 5,691,701 describes a system using multicolored LEDs for sensing the color of a gas, fluid or vapor. The system uses fiber optics for coupling light to and from the gas, fluid or vapor.
Each of the preceding examples describes technology, apparatus or methods for making color measurements or comparisons. However, none of them describes the invention of a small, hand-held and inexpensive calorimeter which can permit an operator unskilled in color analysis to quickly and objectively make consistent color measurements and comparisons.
It is advantageous for such a colorimeter to be compact, inexpensive, and versatile. Versatility is enhanced by the use of designs that avoid specular reflection from glossy or irregular surfaces. It is advantageous for a calorimeter to include an easy-to-use display or other interface so that users with little training can take measurements. It is also advantageous for the user interface to display information in a non-numerical format, so that the user can more readily convey the necessary information verbally.
It is therefore an object of the invention to provide a small and inexpensive apparatus using simple procedures for measuring the color of an object.